Crank Power Changes And Characteristics Across Different Workloads During Stationary Cycling

Stationary cycling is commonly used in rehabilitation for patients with knee osteoarthritis and total knee arthroplasty. Crank power is often determined using a power meter during cycling and typically provided as average value of one second interval during a cycling bout. Understanding detailed characteristics of crank power during a crank cycle may be necessary in exercise prescriptions. PURPOSE: To implement a method estimating crank power from instrumented pedal and examine changes of peak crank power during crank cycle at three different workloads in stationary cycling. METHODS: Nine young, healthy and recreationally active participants performed cycling trials at three workload conditions, 1 kg, 2 kg and 3 kg, at 80 revolutions per minute on a cycle ergometer (818E, Monark). They cycled for two minutes in each condition and three-dimension pedal reaction force (PRF, 1200 Hz) and kinematic (240 Hz) data were recorded during the last 10 seconds. The crank torque was computed as the cross-product of crankarm lengths and PRF vector. The crank power was computed as the product of crankarm angular velocity and crank torque. A one-way repeated measures analysis of variance was used to determine the differences of selected crank power related variables among the three workload conditions (p < 0.05) and post hoc comparisons were performed with Bonferroni adjustment. RESULTS: The statistical results showed significant workload effect for all selected variables, and post hoc comparisons indicated that these variables were progressively changed between three workloads. The peak crank torque was higher in 2 kg (47.1 Nm) and 3 kg (58.5 Nm) compared to 1 kg (35.0 Nm). Peak power was also higher in 2 kg (394.7 W) and 3 kg (500.9 W) compared to 1 kg (296.1 W). In addition, the average crank power during the power phase (0 – 180 deg of crank cycle) was increased from 1 kg (155.9 W), 2 kg (203.9 W) to 3 kg (265.8 W). However, the average crank power during the recovery phase (181 – 360 deg of crank cycle) were all negative and progressively reduced from 1 kg (-64.0 W), 2 kg (-42.5 W) to 3 kg (-28.6 W). CONCLUSION: Peak and average crank power had only an average increase of 30% from 1 kg to 2 kg and 2 kg to 3 kg, although the respective increase in workload was 100%, highlighting the importance of understanding crank power characteristics during the crank cycle.